The present invention relates to a solid material melting apparatus, and more particular, it relates to a solid material melting apparatus suitable to incineration and melting of radioactive solid wastes (including combustible materials, less combustible materials and incombustible materials) discharged from radioactive material handling facilitates such as nuclear power plants.
Combustible radioactive solid-wastes such as rags, clothing and plastics, such as vinyl chloride and incombustible radioactive solid wastes such as metal wastes and thermal insulation materials are discharged from radioactive material handling facilities such as nuclear power plants. The combustible materials and incombustible materials are separated, and incineration processing for the combustible materials and compression processing of wastes or melting processing of melting wastes at high temperature to reduce the volume for incombustible materials have been investigated. Further, for the residues and incineration ashes after incineration of the combustible materials, melting processing has been considered.
As an incineration furnace for processing combustible radioactive solid wastes, an apparatus described in xe2x80x9cResearch and Development on Processing and Disposal of Radioactive Wastesxe2x80x9d (Sangyo Gijutsu Shuppan, p175) have been used generally. In this incineration furnace, combustible radioactive solid wastes are burnt by a gas burner inside of a furnace main body lined with refractories and exhaust gases are discharged from the upper portion of the furnace main body. The exhaust gases are removed with coarse particulates by ceramic filters and high performance filters provided in two stages, and then released out of the system. Further, residues and incineration ashes accumulated at the bottom of the furnace main body are discharged by opening a shutter at the bottom into drams and stored therein.
On the other hand, melting furnaces for processing incombustible solid wastes include two types, depending on the difference of the heating system, that is, a plasma heating type melting furnace and an induction heating type melting furnace. In the induction heating type melting furnace, alternating current is supplied to induction coils wound around a melting vessel, thereby generating radio frequency induced electromagnetic fields at several tens to several hundreds Hz in the melting vessel. Under the effect of the radio frequency induced electromagnetic fields, eddy current is generated to conductive materials disposed in the melting vessel. The solid wastes in a melting vessel are heated and melted by Joule heat caused by the eddy current.
An example of melting processing using such an induction heating type melting furnace is described in Japanese Publication of Patent Application No. Hei 6-64192. In the melting processing, an electroconductive ceramic container is heated by electromagnetic induction to melt solid wastes supplied into the ceramic container and then both the ceramic container and the solid wastes are taken out of the system together for making ingots by cooling.
Another melting processing by using the induction heating type melting furnaces is described in Japanese Patent Publication No. 2503004. In this melting processing, a conductive heat generation body made of carbon filled in the inside of the furnace main body heated by radio frequency magnetic fields and solid materials charged from above the filled layer of the conductive heat generation body are heated and melted by the heated conductive heat generation body. The molten solid materials flow down through gaps formed between each of the conductive heat generation bodies and are then discharged from the bottom of the furnace main body.
Among the prior arts described above, the incineration furnace for treating combustible solid wastes uses burners as a heat source, and so it is difficult to perform melting processing for incombustible solid wastes. Further, as for the handling of incineration ashes, it is necessary to take a countermeasure such as inhibition of scattering ashes.
Then, the melting processing described in Japanese Publication of Patent Application NO. Hei 6-64192 uses a conductive container based on carbon materials, so that it is not suitable to incineration processing of combustible materials in which combustion air is supplied. Further, since the melting processing is batchwise, it imposes a limit on the processing speed for the solid wastes.
The melting processing disclosed in Japanese Patent Publication No. 2503004 can additionally supply the carbon material for the heat generation body, and accordingly, it can also incinerate the combustible solid wastes in principle. Further, since the molten solid materials can be taken out continuously from the bottom of the furnace main body, the processing speed for the solid materials is increased. However, since the exhaust gases are discharged from the upper end of the furnace main body, soots, coarse particulates and combustion gases are exhausted as they are as gaseous wastes. This remarkably increases the burden on the exhaust gas processing. Further, since the solid materials are charged on the filled layer of the conductive heat generation body, dioxins and other noxious gases are generated by incomplete combustion of the solid materials, which may possibly be discharged from the upper end of the furnace main body together with exhaust gases without being decomposed. In addition, there is a possibility that air at low temperature is sucked from a discharging port at the bottom of the furnace to the inside of the furnace along with discharge of the exhaust gases to possibly lower the temperature at the discharging port. Since this may possibly coagulate molten products at the discharging port and clog the same, it is necessary to provide an auxiliary burner or the like.
An object of the present invention is to provide a solid material melting apparatus for suppressing formation of noxious gases such as dioxins and the likes without causing clogging at a discharging port.
A feature of the first invention for attaining the foregoing object resides in an apparatus for melting solid materials comprising a furnace main body having an opening/closing charging port for solid materials and a molten product discharging port at a lower end thereof, and being filled the inside thereof with a conductive heat generation body, and induction coils disposed at the periphery of the furnace main body for induction heating the conductive heat generation body, in which the solid materials supplied to the inside of the furnace main body are melted, characterized in that it comprises a combustion air supply means connected to an upper portion of the furnace main body and an exhaust gas discharging port disposed to a lower end of the furnace main body.
Since the combustion air supply means is connected to the upper portion of the furnace main body and the exhaust gas discharging port is disposed to the lower end of the furnace main body, combustion air is supplied to the upper portion of the furnace main body and exhaust gases generated by the combustion of combustible solid materials are discharged through gaps between each of the conductive heat generation bodies at a high temperature and then discharged from the exhaust gas discharging port at the lower end of the furnace main body to the outside of the furnace main body. Particularly, a portion below the upper end of the filled layer of the conductive heat generation body is at a high temperature. Accordingly, unburned gases and noxious gases contained in the exhaust gases are thermally decomposed while the exhaust gases pass through a high temperature region in the filled layer of the conductive heat generation body so as to promote non-toxification. Accordingly, the amount of dioxins contained in exhaust gases discharged from the exhaust gas discharging port is remarkably lowered and the amount of dioxins discharged to the external environment is also reduced remarkably.
As the conductive heat generation body, those materials being resistant to high temperature and having relatively low electrical resistance value are preferred, and specifically, carbonaceous materials such as graphite, coke, silicon carbide and titanium carbide, high melting metals such as tantalum, molybdenum and tungsten, boride ceramics such as zirconium boride, titanium boride, niobium boride and molybdenum boride, molybdenum zirconia and molybdenum silicide may be used preferably.
A feature of the second invention for attaining the foregoing object resides in that the molten product discharging port serves also as the exhaust gas discharging port.
Since the molten product discharging port serves also as the exhaust gas discharging port, the molten product discharging port is heated to a high temperature by exhaust gases. Accordingly, it is possible to avoid solidification of molten products by cooling the molten product discharging port and to avoid clogging at the molten product discharging port.
A feature of the third invention for attaining the foregoing object resides in the provision of a molten product discharging channel with air tight property connected to the molten product discharging port for introducing the molten products and the exhaust gases, an air tight chamber which is connected to the molten product discharging channel for delivery and entry of a container filled with the molten products flowing through the molten product discharging channel, and an exhaust gas discharging pipeline connected to the air tight chamber for discharging the exhaust gases introduced through the molten product discharging channel into the air tight chamber.
Since the air tight chamber for delivery and entry of the container filled with the molten products flowing through the molten product discharging channel and the exhaust gas discharging pipeline connected to the air tight chamber for discharging the exhaust gases introduced through the molten product discharging channel into the sealed chamber are provided, injection of the molten products into the container and separation of the exhaust gases from the molten products and the exhaust gases flowing in the molten product discharging channel are performed easily to thereby facilitate discharge of the exhaust gases to the outside.
A feature of the fourth invention for attaining the foregoing object resides in that the combustion air supply means comprises a check valve for inhibiting the back flow of the gases flowing in the furnace main body.
Since the check valve is provided, even when the combustion of the combustible solid materials is promoted by charging a great amount of the combustible solid materials into the furnace main body to abruptly increase the pressure in the furnace main body, back flow of the exhaust gases in the furnace main body through the combustion air supply means in the furnace main body can be prevented. Accordingly, the noxious gases contained in the exhaust gases are prevented from being discharged to the external environment without being thermally decomposed through the combustion air supply means.
A feature of the fifth invention for attaining the foregoing object resides in the provision of a heating means for heating the combustion air supplied from the combustion air supply means into the furnace main body by the exhaust gases discharged from the exhaust gas discharging port.
Since the combustion air supplied in the furnace main body is heated by the exhaust gases, the temperature of the combustion air to be supplied into the furnace main body can be elevated, thus promoting the combustion of the solid materials, particularly, combustible solid materials to improve the incinerating performance of the solid material melting apparatus. Since the heat possessed in the exhaust gases is used for heating the combustion air, there is no requirement for providing any additional heating means and therefore the thermal efficiency of the apparatus for melting solid materials is improved. In addition, the temperature of the exhaust gases can be lowered.
A feature of the sixth invention for attaining the foregoing object resides in the provision of a heating means for heating the combustion air supplied from the combustion air supply means into the furnace main body by the exhaust gases introduced by the exhaust gas discharging pipeline.
A feature of the sixth invention can provide the function and the effect obtained by the feature of the third invention, as well as the function and the effect obtained by the feature of the fifth invention.
A feature of the seventh invention for attaining the foregoing object resides in the provision of a filter for removing solid components contained in the exhaust gases discharged from the heating means.
Since the filter is disposed at the downstream of the heating means, exhaust gases at a lowered temperature are introduced to the filter. This can improve the service life of the filter.
A feature of the eighth invention for attaining the foregoing object reside in the provision of a combustion air supply means connected to an upper portion of the furnace main body and a coolant vessel filled with a coolant, the molten product discharging port serving also as a discharging port for exhaust gases, and further, provision of the molten product discharging channel with air tight property connected to the molten product discharging port for introducing the molten products into the coolant vessel, an exhaust gas discharging pipeline connected to the molten product discharging channel above the liquid surface in the coolant vessel for discharging the exhaust gases flowing in the molten product discharging channel and a means for taking out the coagulated molten products from the coolant in the coolant vessel.
According to the feature of the eighth invention, since the molten products are supplied into the coolant vessel filled with the coolant and the molten products coagulated in the coolant vessel are taken out of the coolant vessel, the molten products can be handled easily and can be taken out easily. Further, since the coolant in the coolant vessel constitute a liquid sealing mechanism to provide the effect of a buffer relative to abrupt increase of the pressure in the furnace main body, the safety of the furnace main body can be improved. Further, the feature of the eighth invention can also provide the function and the effect obtained by each of the features according to the first invention and the second invention.
A feature of the ninth invention for attaining the foregoing object resides in the provision of a heating means for heating the combustion air supplied from the combustion air supply means into the furnace main body by the exhaust gases introduced through the exhaust gas discharging pipelines as set forth in the eighth invention.
A feature of the ninth invention can provide the function and the effect obtained by the feature of the fifth invention in addition to the function and the effect obtained by the feature of the eighth invention.
A feature of the tenth invention for attaining the foregoing object resides in that the combustion air supply means in the eighth invention comprises a check valve for inhibiting the back flow of the gases flowing in the furnace main body.
The feature of the tenth invention can provide the function and the effect obtained by the feature of the fourth invention in addition to the function and the effect obtained by the feature of the eighth invention.
A feature of the eleventh invention for attaining the foregoing object resides in the provision of a combustion air supply means connected to an upper portion of the furnace main body and a molten product storage chamber with air tight property having a heating means, the molten product discharging port serving also as an exhaust gas discharging port, and further, provision of the molten product discharging channel with air tight property connected to the molten product discharging port for introducing the molten products into the molten product storage chamber and an exhaust gas discharging pipeline connected to the molten product storage chamber for discharging the exhaust gases introduced through the molten product discharging channel to the molten product storage chamber.
Since the molten product storage chamber with air tight property having the heating means is provided, the molten products discharged from the molten product discharging port of the furnace main body can be stored in the molten product store chamber. Therefore, there is no longer required to provide the air tight chamber for injecting the molten products in the vessel in the third invention, and the constitution of the solid material melting apparatus in the third invention can be simplified. since it is suffice to inject the molten products stored in the molten product storage chamber into the container, the molten product injection operation is facilitated as well.
A feature of the twelfth invention for attaining the foregoing object resides in the provision of a heating means for heating the combustion air supplied by the combustion air supply means into the furnace main body in the eleventh invention by the exhaust gas introduced through the exhaust gas discharging pipeline.
The feature of the twelfth invention can provide the function and the effect obtained by the feature of the eleventh invention, as well as the function and the effect obtained by the feature of the fifth invention.
The feature of the thirteenth invention for attaining the foregoing object resides in a solid material melting apparatus comprising a furnace main body having an opening/closing charging port for radioactive solid wastes and a molten product discharging port at a lower end thereof, and being filled at the inside thereof with a conductive heat generation body, and induction coils disposed at the periphery of the furnace main body for induction heating the conductive heat generation body, in which the radioactive solid wastes supplied to the inside of the furnace main body are melted, characterized by the provision of a combustion air supply means connected to an upper portion of the furnace main body, the molten product discharging port serving also as a discharging port for the exhaust gases, and further, provision of the molten product discharging channel with air tight property connected to the molten product discharging port for introducing the molten products and the exhaust gases thereto, an air tight chamber which is connected to the molten product discharging channel for delivery and entry of a container to be filled with the molten products flowing in the molten product discharging channel and an exhaust gas discharging pipeline connected to the air tight chamber for discharging the exhaust gases introduced through the molten product discharging channel into the air tight chamber.
Since the combustion air supply means is connected to the upper portion of the furnace main body and the exhaust gas discharging port is provided at the lower end of the furnace main body, the combustion air is supplied to the upper portion of the furnace main body and exhaust gases generated by the combustion of the combustible radioactive solid wastes are discharged through the gaps between each of the conductive heat generation bodies at a high temperature from the discharging port situated at the lower end to the outside of the furnace main body. Accordingly, since radioactive materials (for example, cesium) is transferred downwardly, being entrained by the flow of the exhaust gases, from the upper end of the conductive heat generation body filled layer, the degree of contamination on the inner wall of the furnace main body with the radioactive materials is lowered above the upper end of the conductive heat generation body filled layer. Accordingly, maintenance for the furnace main body above the upper end of the conductive heat generation body filled layer can be conducted easily.